Question

4.There is a wall with surface area of 50m2. Suppose that the partition wall is constructed of brick whose transmission loss is taken to be 75dB and a window of 10m2 with the transmission loss of 40dB (i) calculation the average sound transmission loss when the window is closed (ii) calculation the average sound transmission loss when the window is opened fully

Answer 1

Given data,

For wall : Transmission loss (TL₁) = 75 dB , A₁ = 50 m² ,

For window : Transmission loss (TL₂) = 40 dB , A₂ = 10 m² ,

(i) TL when window closed

transmission coefficient of wall and window

As we know the relation between TL and  transmission coefficient ($\tau$)

For wall: TL₁ = 10*log(1/$\tau$₁)

75 = 10*log(1/$\tau$₁)

  $\tau$₁ = 0.00055

For window:   TL₂ = 10*log(1/$\tau$₂)

40 = 10*log(1/$\tau$₂)

  $\tau$₂ = 0.01832

Now, Average transmission coefficient ($\tau$)

$\tau$ = ( A₁ *$\tau$1 + A₂ * $\tau$₂ )/ ( A₁  + A₂ )

= ( 50 *0.00055 + 10 * 0.01832 )/ ( 50 + 10 )

$\tau$ = 0.00351

Now, TL

   TL = 10*log(1/$\tau$) = 10*log(1/0.00351)

= 24.5 dB

(ii) TL when window opened

Now, Average transmission coefficient ($\tau$)

$\tau$ = ( A₁ *$\tau$1 + A₂ * $\tau$₂ )/ A₁

= ( 50 *0.00055 + 10 * 0.01832 )/ 50

$\tau$ = 0.00421

Now, TL

   TL = 10*log(1/$\tau$) = 10*log(1/0.00421)

= 23.7 dB